Add a horizontal bar gauge showing the disk usage % of the 5 most-full
PersistentVolumes in the cluster, using kubelet volume stats already
scraped by Prometheus:
topk(5, kubelet_volume_stats_used_bytes
/ kubelet_volume_stats_capacity_bytes * 100)
Labels show namespace/PVC name. Color thresholds: green <70%, yellow
70–90%, red >90%. Placed at the bottom of the dashboard (y=46).
Bump dashboard version to 3.